Loans and Leases - Summary of Consumer Loans by Payment Status (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Credit Quality [Line Items]
Total Loans	$ 11,626,787	$ 11,247,038
Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	68,312	68,552
Direct Installment [Member]
Credit Quality [Line Items]
Total Loans	1,676,349	1,644,621
Direct Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,608,934	1,565,090
Direct Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	14,356	14,680
Residential Mortgages [Member]
Credit Quality [Line Items]
Total Loans	1,350,502	1,263,053
Residential Mortgages [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	939,368	802,522
Residential Mortgages [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	14,472	15,064
Indirect Installment [Member]
Credit Quality [Line Items]
Total Loans	942,801	875,551
Indirect Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	940,799	872,340
Indirect Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	1,052	1,305
Consumer Lines of Credit [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	970,554	944,631
Consumer Lines of Credit [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	1,920	1,796
Other [Member]
Credit Quality [Line Items]
Total Loans	40,809	41,290
Other [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	40,809	41,290
Originated Loans [Member]
Credit Quality [Line Items]
Total Loans	10,244,577	9,666,145
Originated Loans [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Total Loans	1,623,290	1,579,770
Originated Loans [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Total Loans	953,840	817,586
Originated Loans [Member] | Indirect Installment [Member]
Credit Quality [Line Items]
Total Loans	941,851	873,645
Originated Loans [Member] | Consumer Lines of Credit [Member]
Credit Quality [Line Items]
Total Loans	972,474	946,427
Originated Loans [Member] | Other [Member]
Credit Quality [Line Items]
Total Loans	$ 40,809	$ 41,290